1. Technical Field
The present invention relates to a visualization device. In its broadest sense, the invention falls within the field of visualizing objects or materials on a screen with the aid of computer-graphic techniques, wherein a digital representation of an actual material or of a surface of an actual object is applied to (rendered onto) a virtual object of any form, and the appearance of the virtual object simulated in this way is then displayed on the screen under user-selected illumination conditions and at user-selected observation directions.
2. Background Art
The appearance of a material is understood to mean the visual impression of a physical material, for example the surface of an object, which is given by the entirety of all its chromatic and structural as well as material properties under different illumination and observation conditions. Material properties include for example translucence. Appearance data are a digital representation of the appearance of a material. Rendering is understood to mean computer-graphically applying data which describe the appearance of a material, i.e. appearance data, to the surface of a virtual material or object, and displaying the virtual material or object. The terms “appearance”, “appearance data” and “rendering” have established themselves in the relevant specialist circles and are therefore also used in the present text.
In creative applications such as, for example, product design, comprehensive databases of appearance data are required. Known examples of appearance data and/or datasets include the so-called bidirectional texture function (BTF) and the spatially varying bidirectional reflectance distribution function (SVBRDF). In order to obtain a set of appearance data such as for example a BTF or SVBRDF of an actual material and/or the surface of an actual object, a representative surface region of the object in question is colormetrically gauged pixel-by-pixel for a large number of illumination directions and observation directions, typically by using a number of digital colour cameras and a complex illumination system comprising hundreds of point light sources which are arranged in a distribution over the hemisphere above and/or below the material to be gauged.
Appearance data available for an actual material are used for visualization, i.e., graphically displaying the material on the screen, as rendered onto a virtual object of any form, under any desired illumination condition and any desired observation direction, by means of digital rendering techniques which use the appearance data as input data. Suitable rendering techniques and corresponding software are well-known in computer graphics and are not the subject of the present invention. It may merely be mentioned that such rendering techniques can extract colour values (colour reflectance values) from the appearance data for each pixel of the actual material, for any given illumination direction and any given observation direction, wherein intermediate values can be calculated by interpolating between the values contained in the appearance data.
In all practical applications of said visualization techniques, as good a match as possible between the appearance of the underlying actual material and/or object and the virtual object onto which the appearance of the actual material has been rendered is sought, and under all illumination and observation conditions. If it is assumed that the rendering techniques used are themselves sufficiently powerful, then the virtualisation quality depends primarily on the quality of the underlying appearance data. In addition, some actual materials are less suitable for simulated visualization than others. Ultimately, the virtualisation quality can only be assessed by visually comparing the underlying actual material and/or object with the virtual object, wherein however this visual comparison should as far as possible be made under controlled illumination and observation conditions.
Against this background, it is an object of the invention to provide a visualization device which enables a direct visual assessment and comparison of an actual object with a virtual object which is displayed on a screen by computer-based rendering of digital appearance data of the actual object. The visualization device is in particular desired to enable an assessment and/or comparison under controlled illumination and observation conditions.